Method of treating hydrocarbon oil



Sept. l, 1936. H. v.' ATWELL METHOD OF TREATING HYDROCARBON OIL Filed Jun? lO, 1933 Patented Sept. 1, 1936 UNITED STATES lPATENT OFFICE METHODV OF TREAlIIlTG HYDROCARBON Harold V. Atwell, White Plains, N. Y., assignor to Gasoline Products Company,

Inc., Newark,

This invention relates to processes for the production of relatively light hydrocarbon oil, such as gasoline, from relatively heavy hydrocarbon oil, and pertains more particularly to processes of this character wherein part of the once cracked oil is recycled in order to bring it to the desired specifications.

Prior practice has clearly indicated that, while certain types of hydrocarbon oils may be eiiiciently converted by cracking, into lighter products, e. g. those in the gasoline boiling range, under relatively high pressure, other oils should be cracked under lower pressures, in order to avoid the formation of excessive amounts of coke and undesirably heavy products of polymerization.

It has been found that relatively high pressures tend to cause more undesirable polymerization of recycle stock, for example, than of virgin stock, and accordingly Various proposals have been made for the cracking of the recycle stock in a separate zone wherein different conditions are imposed, than on the virgin stock. This would necessitate increased investments for the additional equipment necessary, with the result that in some cases the separate treatment of recycle stock could hardly be justied from a financial viewpoint.

With these points in mind it is an object of my 'invention to provide a process for the treatment,

in a single cracking zone, of a plurality of oil `vreference numerals 3, 5, 8, and I Il indicate respectively a furnace or heater, reaction chamber or digester, separator, and fractionator, through which the oil to be treated is passed in the usual cycle. -Fresh charge, from a source not shown, is forced through line I, by pump 2, into heater of furnace 3, which is preferably of the tubular type. The heated oil emerges from the furnace 3 through pipe 4, at a temperature which may vary considerably, for example from 800 to l200 F., but most suitably lies in the range of 850 to 975 F., preferably about 950 F., and is introduced into reaction chamber or digester 5, of the conventional type, wherein cracking thereof takes place, with resulting formation of lighter and heavier products. The temperature and time of passage of the oil through heater 3 may be sucient to produce a considerable amount of cracking therein, or the major percentage of conversion may 5 take place in chamber 5. Alternatively, the cracking conditions may be so selected as to cause all of the cracking to take place in the coil, the reaction chamber being eliminated. These operations of heating and digesting are suitably carried out l0 at a fairly high pressure, e. g. from 500 to 3000 pounds per square inch, preferably about 1200 pounds per square inch, but higher or lower pressures may be provided. y After undergoing cracking in the digester 5 the hot products of con- 15 version are passed through line 6, having reducing Valve 'I, into separator 8, in the usual manner. In the separator vapors separate from liquid residue, this residue being drawn off through line I6 for storage, or for any further Couven-.20 tional treatment, 'while the vapors are passed through pipe 9 into fractionator I0, wherein the vapors are caused to flow lthrough bubble trays, or other fractionating devices, with resulting partial condensation thereof. Vapors of the desired *25 end point pass off through vapor line I I and con- 'denser I2, the condensate being collected in receiver I3. A cooling coil I4 is provided for regulating the character of the vapors passing off from fractionator I0, and a similar cooling coil, I5, is 3o furnished for'separator 8. Fresh charge or any other cooling medium may be forced through these coils.

Liquid reflux condensate formed in fractionator Ill is withdrawn therefrom through valved line -35 I'I and is forced by pump I8 into line I, for mixture with the fresh charge, and recycling through the system. A portion of this condensate may be diverted from the process through valved line I9 and cooler 20, into receiving drum 2|, for 40 any desired further treatment, or use. And if desired additionalv charging stock of a different type may be introduced through auxiliary charging line 22 having pump 23. Valves 24, 25, 26, 2I, and 28 provide the necessary control where- 45 by the relative volumes of the different stocks undergoing cracking may be regulated.

The ratio of recycle stock to fresh charge is so selected that cracking of both stocks is accomplished without the formation of such large50 quantities of coke and heavy polymers, as would take place without the selection of the proper ratio. The ratio used, in accordance with my invention is such that the partial pressures on the two stocks undergoingtreatment, are those 55 which correspond to the pressures found most suitable for the individual treatment of these stocks in separate cracking zones. Thus, if it has been found that a certain fresh charging stock is most successfully cracked under a pressure of, for example, 800 pounds per square inch, and that most ecient cracking of the recycle stock derived from that operation may be carried out'at'a lower pressure, of, for example, about 400 pounds per square inch, then where both stocks are being cracked in the same heatingc'dil or furnace, by the recycling ,processnthe amount of recycle stock should be about one-half of that of the fresh charge, the recycle ratio then being one to two. By so selecting the ratio it is determined that the partial pressures onthes'e separate stocks while undergoing conversion at high temperature, i. e. upon approaching .the iend :of

the heating coil or during passage through .the

reaction chamber, will be approximately the same as the pressures found 'most suitable in separate operations. While it Vis true that the molecular weight 'of the Vrecycle stock will be somewhat heavier than that'of the fresh charge, this factor maybe disregarded, 'substantial'equality being assumed. -On the basis of this assumption the ratio of recycle stock vto fresh charge would be substantially the same-as that :desired for the corresponding rcracking pressures. In the case assumed above, if 800 and 400 pounds pressure are Vfound -most suitable, respectively, for the cracking of fresh:char.ge and recycle stock, 'then according to my invention the-oil zmixture inthe ratio of one part :recycle Astock 'to two :parts fresh charge Awould be cracked under a total pressure of 1200 pounds vper square inch. The same lprinciple applies `Where two different :fresh charges are Vsubjected to -cracking fin a :single coil, recycling being `used ortnot, as "desired, 1f any-stock iszrecycled thentheftotalpressure would have to Abe apportioned among the three'diierent stocks undergoing :.cracking, `in the :proper ratio to give the desired ,partial pressures Operation ably-from 80011301200" .F., and -in any event 'high venough to `vaporize most of 'the charging stock, preferably about 875 to 975 F., the outlet :pressure on the theater fbeing, yforexampl'e,'about 1200 pounds `per square inch. During `:its Npassage through the heater `the "oil 'may becracked to a Agreater or ilesser rdegree, or :in certain instances it maybe-desirable Vto :heat the oil-.so quickly that very little cracking takes placein the heater. The 'outletpressurezon the heater may vary fover a relatively wide frange, 1e. vg. (from500 -to v3000 pounds per-square linen-depending :upon the type of stockrbeing cracked, the 4time of passagefand 'the character :o'f iinal product desired, fbut for the rproduction :of :gasoline from 'a charging -stock ofthe character mentioned, `a pressure of about 1200 pounds per-square-inch is preferable. The highly `heated stock .fi-s zpassed 'from :the heater ,through the "digestion'chamber 5, Awithin which the soaking or Iadditional fcracking takes place without the :addition lcf lheat, under substantially fthe same pressure `as :that fof :the rheater, andthe resulting :products of fconversion are passed through ireducing -valve :1 into .the separator 8,

which is .maintained lunder :'a considerably lower pressure than that of the heating and digesting Zones. The pressure in the separator 8 may be, for example, about 200 pounds per square inch, although, as in the case of the cracking zone, this pressure may vary over a fairly broad range, for example, from 50 to 400 pounds per square inch, depending upon the character of the nal product being produced. Most suitably, however, the `pressure will be about 200 pounds per square inch in the case of the specific charging stock mentioned. In the chamber 8 vapors separate from liquid residue, the former being cooled by coil l5 to condense heavier undesired portions thereof, while the remaining uncondensed vapors pass over 1into the fractionator lil and are there dimuch reilux condensate is produced to be usedv entirely as recycle stock, a portion of it :may 'be ,diverted through -line 4|-9 'to receiver 2l, while in those cases where the reflux -condensate is deiicient -in quantity, additional charge may be introduced through line 22, thischarge being either ofthe same type as the recycle stock or of a different type. be one-half that of the lfresh .charge in this specic instance, whereby the :partial .pressures exerted on the two lstocks will 'be approximately 400 pounds and 800 pounds per -square inch :respectively. In accordance with :my invention when Ioperating under ordinarycracking conditions of temperature and pressure ongas oilf-or similar Vcharging stock the recycled stock fshould preferably not-exceed one-half .the fresh charge, quantity. When :extremely high rates `of cracking are secured, e. g. in excess :of 50% fper pass, all of the recycle stock may be returned .-to the cracking-operation. When the recycle ratio is-selected inzaccordance with my invention as described hereinbefore the cracking rate may be However, in the Vcase of conventional moderate f temperature and pressure cracking wherein a conversion to products in the gasoline -boiling range, of about 15 to 25% per pass is obtained, a portion of the reilux Ycondensate which is 'ordinarily recycled will have to :be ydiverted from the process in order to establish balancedconditions. Preferably not oVer'one-half of 'this vstock is recycled -under these lcracking conditions.

If it is desired to `crack three stocks infa Asingle coil, the optimum cracking pressures thereof being found by experiment, 4800, 400, and 200 pounds per square inch, for'example, these Vstocks should be charged to the cracking Zone in quantities bearing the ratios of four to two to one in the order given, under a total pressure of about 1400 pounds per square'inch. While I havementioned hereinbefore that the recycle stock will ordinarily not `have 'changed in molecular -weight suiliciently to require consideration of that ipoint The amount of recycle stockmayl yin :selecting the ratios, in certain instances and,

with particular charging stocks the molecular weight of the recycle stock may be changed sufficiently to justify a correction of the particular ratio thereof, and in the case Where two different types of charging stocks are subjected to conversion in a single coil, these stocks being either virgin or cracked, or both, corrections for the difference in molecular weight may be necessary, the higher the molecular weight the greater the quantity of that stock needed to produce the desired partial pressure.

While I have particularly described the invention in connection with one conventional form of cracking system wherein a high pressure digestion chamber is used, the invention is applicable as well to` other types of cracking processes, wherein no enlarged reaction `chamber is used or wherein heating of the charge oil is brought about by admixture therewith, of highly heated fluids. The specific example given is intended merely for illustration, and it should be understood that various vmodifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

l. The process of treating hydrocarbon oil which comprises passing a clean gas oil charging stock through a heating zone wherein the temperature is raised to a value in excess of 900 F. in the absence of added hydrogen, while maintaining a pressure in excess of about 1000 pounds per square inch on the oil leaving the heating zone, whereby conversion of the oil into lighter products takes place, separating the resulting cracked products into vapors and a liquid residue, separating said vapors, by partial condensation, into a desired light vapor and a. condensate, and recycling condensate so separated for cracking with the fresh charge, and preventing the quantity of recycled condensate from exceeding one-half that of the fresh charge, said pressure first-mentioned being the sum of the pressure desired on the fresh oil and the pressure desired on the recycled condensate and said pressure desired on the fresh oil being at least double that desired on said condensate.

2. The process of treating hydrocarbon oil which comprises passing a mixture of fresh charging oil and recycle stock through a heating zone wherein the oil is raised to a vapor phase cracking temperature and subjected to conversion, separating the resulting cracked products into vapors and a liquid residue, subjecting said vapors to partial condensation to condense undesirable heavy fractions therefrom and leave vaporized the desired fractions, maintaining on the oil undergoing cracking a pressure equal to the sum of the pressure desired on the fresh oil and the pressure desired on the recycle stock, said pressure desired on the fresh oil being at least double said pressure desired on the recycle stock, returning to said heating zone as said recycle stock condensed undesirably heavy fractions of said vapors, in the same proportion with respect to the quantity of fresh charge as said pressure desired on said recycle stock bears to said pressure desired on the fresh oil, and preventing the quantity of recycle stock returned to said heating zone in mixture with said fresh charging oil from exceeding one-half that of said fresh charging oil, by diverting any excess recycle stock from the process.

HAROLD V. ATWELL. 

